Conventionally, an air conditioner for a vehicle uses an air passage opening and closing device as described in Patent Document 1. In such a conventional technique, an air passage defined in a case is opened or closed by sliding a slide door that has a door body having a plate shape.
When the slide door is located to close the air passage, a case-side sealing surface provided with the case is in contact with a plate surface of the door body such that a sealing performance is produced.
The slide door is constituted as an air mix door adjusting a temperature of air that is blown into a passenger compartment. Specifically, the slide door is located between an evaporator and a heater core in the case and adjusts a volume ratio between an air volume of warm air after passing through the heater core and an air volume of cool air flowing as bypassing the heater core.